XFi fan turns on, resets

Why at radom times, always during the day while I'm using it, does my wifi decide to possibly update?  The internal fan turns on, it's warm, and I lose internet.  I'm only a light web surfer and email person. Honks me off, so I unplug, sit 1 min, plug in, wait 5 minutes, and all is good.  This happens probably 1x a week, mid afternoon?  Is there a setting to change this to middle of night?  Thanks